1. Introduction
The lenses of human and animal eyes are subject to damage by physical or other external trauma whether accidental or otherwise and by the formation of cataracts. It has been common practice for many years to surgically remove such damaged lenses. An eye with the lens removed is said to be in the aphakic condition. Subsequent to intracapsular or extracapsular lens extraction, the aphakic eye does not have the ability to focus light with the result that the retina receives only a blurred image. Contact lenses, spectacles or a combination of the two have been used in the past with varying degrees of success to focus the light rays to restore vision. The use of contact lenses and eye glasses to overcome aphakia is subject to the fundamental drawback that such devices are located outside of the eye which results in a shift of the focal point from the natural position within the eye. This results in distortion and/or a change in size of the image. Moreover, eyeglasses cannot restore normal binocular vision if the other natural eye remains and contact lenses must be in continuous use to maintain vision in the aphakic eye.
Cataracts are a common disorder of the eye and are the second leading cause of blindness in the United States. A cataract is a physical change in the structure of the lens of the eye which causes transformation of the normal transparent lens to a cloudy or opaque state. The function of the lens is to focus light rays to form a perfect image on the retina. Cataracts interfere with the focusing of the light rays causing the image to become blurred and eventually leading to blindness if unattended. The opacities caused by cataracts are often not distributed uniformly so that the lens has both opaque and clear areas. Therefore, the degree of loss of vision depends on the size, location and density of the opacities.
There are several basic types of cataracts including congenital cataracts; traumatic cataracts caused by accidental injury; and most common of all, senile cataracts, most prevalent in the elderly. It is not known why senile cataracts develop and the process may proceed over a period of months or even years before treatment is required. At present, the only successful treatment is surgical excision and replacement of the cataractous lens.
The lens of the human eye contains a hard central nucleus within a cortex. Disruption of the perfectly aligned fibers of the cortex and nucleous causes opacities. Large areas of the cortex and nucleus thus gradually become opaque until the image on the retina is blurred. At this point, the cataract has progressed to a stage where some of the resolving power of the eye is lost due to the damage to the lens.
A cataract is treated by relatively simple surgery under local anesthesia in which the lens material affecting vision is removed. Approximately one half million Americans undergo such surgery every year, cataract or lens removal being the most frequently performed operative procedure by ophthalmic surgeons in the United States.
During the operation, the surgeon views the operation site through a high powered microscope which greatly magnifies the eye to facilitate the procedure. The eye is kept moist with physiological saline throughout the procedure.
In the past, standard procedure for removing the damaged lens involved first dilating the pupil and then making a half circle incision at the junction of the sclera and the clear cornea. The upper half of the cornea was reflected and the iris was retracted to provide access to the entire lens. The lens was then removed by one of several techniques. For example, the lens may be drawn or eased out through the incision by means of a cup-shaped suction fixation instrument called an erysiphake. The lens may also be removed by a cryoadhesion (freezing) technique known in the art. Such procedures are known as intracapsular techniques, since the entire lens and capsule is removed.
Another method is to excise the anterior capsule, shell out the nucleus, and vacuum out the cortex. This is an extracapular technique.
Regardless of the technique of removing the lens, the incision must be large enough for this purpose and must be sutured to complete the operation. The patient requires from about 48 hours to one week to convalesce from such operations due to the discomfort and irritation caused by the large incision.
In recent years intraocular lenses have been developed for implantation in the eye after the cataractous or otherwise damaged lens has been removed, thereby eliminating the need for contact lenses or eyeglasses after surgery.
The first intraocular lens was implanted in a human eye in 1949. From its inception, the intraocular lens has had a tumultuous history. The controversy has centered around the placement, location, design and surface quality of the artificial lenses.
In Applicant's above-referenced prior application, an expansile artificial intraocular lens was disclosed, that is, a dry lens capable of insertion through an incision of minimal length which lens expands upon implantation to an optically correct lens. By minimizing the incision through which such a lens can be implanted; discomfort, irritation and, therefore, convalescence are reduced. Having generally set forth the requirements for expansile lenses in such prior application, and expansive lens having particularly novel features is hereafter set forth.
2. Field of the Invention
This invention relates to the field of intraocular lenses and more particularly to expansile intraocular lenses. Specifically, the invention relates to an artificial intraocular lens having novel features of construction and arrangement which serve to center the optic portion of the lens on the optic axis.
3. Description of the Related Art
Existing intraocular lenses are made of a clear, hard plastic material or glass, usually plano-convex. Such lenses are ground and polished to predetermined specifications for the range need for human lens replacement. Over the years such lenses have had a broad range of forms and sizes. Basically, such lenses are a disc with or without suspensory projections about its periphery. The projections, in whatever form, suspend the lens within the anterior or posterior chamber. Such projections are commonly called haptic loops. These loops emanate from the periphery of the optic or clear portion of the lens. Such haptic loops may be curved, or be in the form of J's. The thin loops can be made of prolene (polypropylene) and fit into holes in the optic or lens. The loops are then permanently affixed to the lens.
Whatever form the lens takes, it must be oriented along the visual axis within the eye. The visual axis is an imaginary line which passes axially through the center of the lens and extends through the pupil and cornea. The lens must be centrally oriented along this axis in the path of the light to the retina. The curved front and back surfaces of the lens or disc must be positioned on the same axis to provide an optically correct orientation. The purpose of the haptic loops is to anchor the lens in a central position along the visual axis. The curved portion of the loops contact the chamber walls and hold the lens in place.
The original intraocular lenses posed many problems associated with their use. Many such lenses, having loops of nylon or of plastic also showed marked biodegradation of the loops, after prolonged periods of use, where the chamber angle was contacted due to the biological reaction between the loop material and adjoining structures. Many loops were digested completely leaving the lens free floating in the chamber and no longer aligned in the visual axis. Other problems occurred as the result of the surface finish on many of the early implants. Analysis showed sharp grooves in the surfaces formed from lathe polishing. Edge aberrations of the lenses also caused chronic irritation. It was also found that lenses of too large or too small a size caused corneal dystrophy. Examination of these early lens implants paved the way for the current knowledge of design requisites for intraocular lenses. Today, the vast majority of cataract operations performed in the United States involve implanting intraocular lenses.
Cataract surgery incorporating implantation of an intraocular lens is similar to the operation performed without implantation. However, there is no single method followed by all surgeons. Generally, a large incision, approximately 10 mm, is made in the conjunctiva and limbus where the cornea and the sclera meet. The cataractous lens nucleus is then shelled out. The remaining cortex is aspirated to leave a clear lens capsule. A relatively new process called phaco-emulsification allows this incision to be reduced to 3 mm. Phaco-emulsification, an extracapsular technique, involves ultrasonic fragmentation of the lens into small particles. Once this has been accomplished, the particles are removed by suction leaving a clean capsule free from cataractous material, and only a small opening in the eye. However, the present relatively large-sized implants require enlarging the incision to at least 7 mm to accommodate the introduction of the intraocular lens. The lens is placed and positioned in the posterior chamber to provide an optically correct visual axis. The loops rest and anchor the lens against the capsule walls. Positioning the lens is a delicate technique with surgeons using different lenses and procedures. However, one procedure which is typical is to anchor or fix the lens in position by suturing one or more of the haptic loops. Alexeev, U.S. Pat. No. 4,316,292 issued Feb. 23, 1982, describes a lens wherein one haptic loop is stitched.
While intraocular lenses are becoming popular in present day ophthamology, many designs are still experimental and it is not known how long the new lenses will last in the human eye. Ophthamologists usually suggest that older patients have the lens implant. Controversy still remains as to the design and placement of the lens. Aphakic patients must still go through this intricate operation to accurately position the lens and must still convalesce for many days until the incision heals.
Furthermore, by virtue of the hard plastic composition and large size of presently available intraocular lenses, they are technically demanding to position properly. The haptic loops emanating from the lenses are also awkward to manipulate and may cause trauma to the eye if they are not carefully inserted.
The initial incision in the cornea still tends to be large, sometimes more than 7 mm, to accommodate the lens and the protruding loops. The lens is slipped through the large incision, loop end first, and positioned in the posterior chamber. An incision of this size requires post operative care and causes irritation and consequent discomfort to the patient.
In view of the foregoing, it is apparent that the need for heavy glasses or contact lenses after cataract surgery has been eliminated. However, serious problems still exist with the lenses themselves and also with the operating procedures. A considerable body of patent art exists in this field of which the following is representative.
Thiele, U.S. Pat. No. 3,553,299 issued Jan. 5, 1971, describes a process for making replacement eye lenses by dissolving the lenses of the eyes of warm blooded animals and processing the resulting material to form a gel from which the replacement lens is formed.
Cordrey et al U.S. Pat. No. 3,943,045 issued Mar. 9, 1976, describes a process for making hydrophilic polymers suitable for use as contact lenses or surgical implants, among other things. Highgate, U.S. Pat. No. 3,961,379 issued June 8, 1976, also discloses hydrophilic polymers such as polymethyl methacrylate and hydroxyethyl methacrylate which are suitable for use in making contact and prosthetic lenses.
Flom, U.S. Pat. No. 3,991,426 issued Nov. 16, 1976 describes artificial intraocular lenses for implantation in the posterior chamber of the eye. This reference also summarizes in considerable detail the history and development of artificial intraocular lenses and the need for them.
Banko, U.S. Pat. No. 4,253,199 issued Mar. 3, 1981 discloses deformable lenses for surgical implantation which are composed of a hydrophilic acrylic polymer, such as "Hydron", which is used for soft contact lenses. The lenses are filled with a suitable liquid or semi-viscous material such as a sterile solution or gelatin, or Ringer's solution, and sealed prior to implantation.
Tennant, U.S. Pat. Nos. 4,254,509 and 4,254,510, each issued Mar. 10, 1981, disclose artificial intraocular lenses composed of rigid materials such as polymethyl methacrylate or soft materials such as hydroxyethylmethacrylate; the rigid material being used for the lens only or for the entire implant and the soft material being used only for the supporting members in other embodiments.
Kelman, U.S. Pat. No. 4,092,743 issued June 6, 1978, describes an artificial Intraocular lens designed in an attempt to minimize incision length. Since the Kelman lens is full size upon implantation, the minimization of incision length is still not complete. Further, it has been found that this lens was too small in the eye, permitting passage of unfocused light rays around the edge of the lens.
The entire disclosures of U.S. Pat. Nos. 3,943,045; 3,961,379; 3,991,426; 4,092,743; 4,253,199; and 4,254,509 are hereby incorporated herein by reference.
It is apparent from the foregoing, that while much work has been done in this art, there still remains a need for an improved intraocular lens and an improved, less traumatic procedure for the implantation of such lenses.
As described herein, and as was disclosed in prior application Ser. No. 520,187, which is incorporated herein by reference, an expansile intraocular lens is used to overcome many of the above problems. Such lens is implanted in a dry or xerogel state through a minimal width incision, such as that used in the extracapsular technique of phaco-emulsification, and becomes hydrated by the fluid present in the eye. The term "dry state" as used herein includes a lens having a wetted outer surface for ease of implantation. However, the bulk of the lens is in the xerogel state. Hydration of the lens results in the expansion or swelling of the lens to an optically correct lens.
To minimize movement of an implanted expansile lens, a patient has to remain still until sufficient expansion has occurred to ensure relative centering of the lens. It is, therefore, desirable to have an expansile lens which becomes centered relatively quickly, preferably immediately, upon implantation.
Koeniger, U.S. Pat. No. 4,449,257 issued May 22, 1984 and filed May 3, 1982, appears to disclose an intraocular lens made from HEMA. No structure or technique is disclosed for immediate centering of the lens upon implantation. Further, since the lens is designed so that only an optic replaces the eye's natural lens, fixation of the lens is said to be obtained by frictional engagement with the capsule. Consequently, due to physical demands of a lens of that size, it cannot be inserted through a minimal width (approximately 3 mm) ocular incision.
It is an object of the invention to provide an intraocular lens which does not require long time periods for centering but which is self-positioning on the optic axis immediately on implantation.
It is still another object of the invention to provide an improved intraocular lens and method for its implantation which reduces the size of the incision required and thus trauma to the eye and consequently reduces convalescent time and discomfort to the patient.
It is a further object of the present invention to provide an intraocular lens which expands after implantation to form a soft lens with soft haptic loops incapable of damaging the capsule interior and which is thus suspended centrally along the visual axis of the eye.
It is a further object of the invention to provide an expansile intraocular lens having haptic loops which center the optic portion of the lens along the visual axis of the eye and which become soft upon implantation in significantly less time than the optic portion.
It is a further object of the invention to provide an expansile intraocular lens preferably having two haptic loops positioned in diametrically opposed locations about a central optic portion, wherein the haptic loops are shaped to conform to and gently engage the capsular sac at diametrically opposed points providing support for the central optic portion.